Terms were not revealed.
Thornton, 30, is averaging 4.7 points and 3.5 rebounds in 17.1 minutes per game off the bench in her first season with the Liberty after being acquired from the Dallas Wings in a three-team trade in January that also involved the Connecticut Sun. She is shooting 44.4% from the field.
"From the moment KT arrived in Brooklyn, she has exceeded the standards of resilience, physicality, consistency and character that embodies the New York Liberty," general manager Jonathan Kolb said in a statement. "We look forward to continuing this journey with KT where she will undoubtedly play a key role here for years to come."
In her career with the Washington Mystics (2015), Wings (2016-22) and Liberty, Thornton is averaging 7.4 points, 4.5 rebounds and 1.3 assists per game in 229 regular-season games.